1. Field of the Invention
The invention relates to an apparatus and to a method for level control in a fluid tank. Apparatuses and methods of this kind can be used, in particular, in cleaning appliances for cleaning washware. For example, the apparatus and the method can be used in dishwashers for dishes, containers or similar washware, in particular in dishwashers for commercial use. In addition to single-chamber dishwashers, the invention can advantageously be used in multi-chamber dishwashers too, for example in conveyor-type dishwashers. The invention can be used with particular preference in conjunction with treatment apparatuses for removing impurities from a cleaning liquid. For example, a treatment apparatus of this kind can comprise a device for separating dirt, preferably a centrifugal separator for separating impurities using centrifugal force.
2. Description of the Background Art
Cleaning apparatuses for cleaning washware are known from the extremely wide-ranging fields of natural sciences, engineering and medical technology. In the text which follows, reference is made to dishwashers in particular, but other types of cleaning appliances, for example cleaning appliances for cleaning medical equipment, articles for patient care, cleaning appliances for cleaning containers and trays or other types of cleaning apparatuses, can benefit from level control according to the invention. In general, the invention can also be used in other types of fluid systems in which level control of a fluid in a fluid tank is important.
The treatment of cleaning liquids, for example water with or without added assistants (for example detergents, rinse aids or the like) plays an important role in many cleaning apparatuses. Treatment apparatuses which are designed to remove impurities, for example liquid or solid impurities (for example suspended particles), from the cleaning liquid are often provided for this purpose. As an alternative or in addition to, for example, filters which can carry out the treatment operation, the technique of centrifugal separation is often used to treat cleaning liquids. Such dirt separators which are based on centrifugal separators are often also called “cyclones”. Centrifugal separators of this kind can be used particularly advantageously in conjunction with dishwashers, as is known from DE 1 965 828 A1, DE 1 703 612 A1, DE 660 23 00 U, DE 198 36 739 A1 or DE 1 250 979 A1. In the text which follows, reference is made to all of these documents for possible refinements of a centrifugal separator and for functional principles of such centrifugal separators. Centrifugal separators are designed to make the cleaning liquid to be purified eddy, for example in the form of one or more vortices. By virtue of this eddying, impurities are separated off due to their inertia.
If a tank of a dishwasher, for example a washing tank, is equipped with (that is to say is connected to) a treatment apparatus of this kind, in particular a centrifugal separator, in order to clean the cleaning liquid continuously or in specific cycles, it is often necessary for a partial quantity of the cleaning liquid which is routed through the treatment apparatus to flow out of this treatment apparatus together with the separated dirt, for example as part of a circuit. However, this reduces the level of cleaning liquid in the associated supply tank. This loss should be permanently compensated for, so that the ability of the cleaning apparatus to function is maintained.
This level compensation can be performed in various ways. For example, a level sensor can be used to detect whether the level in the supply tank has fallen below a permissible quantity. If this is the case, a refilling system can be put into operation. However, this means increased outlay on equipment.
In another procedure, cleaning liquid flows, for example out of a downstream tank of the cleaning apparatus, into the supply tank, from which the treatment apparatus is fed, and supplements the filling level. However, if the quantity of water flowing in is not sufficient for operation- or method-related reasons, a circulation pump for cleaning and/or the circuit through the treatment apparatus, for example, has to be disconnected. This results in the disadvantage that there is no longer any cleaning function in the corresponding section of the cleaning apparatus in this case, or that the treatment of cleaning liquid is put out of operation.
A further disadvantage of the described procedures is that an increased quantity of cleaning liquid is consumed. For example, continuous refilling of water to maintain the function of the cleaning apparatus can be associated with increased water consumption. Although substantially no water is lost during the washing process in the apparatus described in DE 1 250 979 A1, this advantage has to come at the expense of additional complexity of a dirt-collection container at the waste-water outflow of the centrifugal separator and an additional stop valve at the outlet of this dirt-collection container.
Overall, the apparatuses known from the prior art therefore have the disadvantage that a considerable amount of additional outlay on a sensor system and additional apparatuses is required in order to control the liquid level in the supply tank, if any such control is provided at all, and this considerably increases the costs and the technical outlay on the cleaning apparatus overall. This also results in an increased susceptibility of the cleaning apparatuses to faults.